This invention is directed to a seal for assuring that a container is tamper-resistant and, in particular, to a seal which can be scanned ultrasonically to determine its integrity and its identity.
Over the years it has been desirable for many reasons to assure that containers are tamper-resistant, whether they be letters, parcels, boxes, and all sorts of other enclosures such as trucks, trailors, boxcars and the like. The most commonly used seal is the wire or customs type seal in which a wire or cable is joined such as by twisting or crimping in a tamper resistant closure. This type of seal, which would have an identification number printed or stamped on it, can easily be replaced and therefore the enclosure must be inspected to be sure that it has not been entered.
This general lack of security is not satisfactory, particularly in applications such as the storage of spent fuel in nuclear establishment. Seals used in these applications must be under water and, therefore, it is desirable to be able to inspect the integrity of the seal and, thus, indirectly the enclosure, both remotely and without removal of the seal. Once the integrity of the seal is determined, the inspection must also reveal the unique identity of the seal.
It has been found that ultrasonic methods lend themselves to the inspection of seals under conditions in which direct inspection is not possible. One such method is described in British Pat. No. 1,278,749 which issued to the European Atomic Energy Community. In accordance with this patent, the identity of the seal is incorporated into the seal by a random distribution of material in the seal body which provides a unique signature when scanned by an ultrasonic reader. Thus, it may be determined whether the seal has been changed, however, if the seal is broken and repaired, the identity of the seal is not altered. Only the identity of the seal can be initially determined and its integrity requires a separate check.